Method for estimating long term end-of-life characteristics using short-term data for lithium/silver vanadium oxide cells
First Claim
1. A method for estimating the discharge curve of an electrochemical cell, comprising the steps of:
- a) subjecting a first cell to a first shorter-term accelerated discharge test having a shortest total time on test, thereby generating a first discharge curve;
b) subjecting a second cell to a second shorter-term accelerated discharge test having a longer total time on test than the first cell, thereby generating a second discharge curve;
c) subjecting a third cell to a longer-term accelerated discharge test having a longer total time on test than either the first or second cells, thereby generating a third discharge curve, wherein the first, second and third cells are of a similar chemistry and construction;
d) offsetting the second and third discharge curves so that they intercept with the first discharge curve at a pre-determined similar percent depth-of-discharge;
e) calculating a first and second series of slopes for the first and second cells, respectively, from the intercept to an end percent depth-of-discharge at incremental depths-of-discharge;
f) calculating a rotational angle between the first and second series of slopes at each incremental depth-of-discharge; and
g) utilizing the rotational angles from step f) to estimate the third discharge curve from the intercept point to the end percent depth-of-discharge.
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Abstract
The present invention is directed to a method for analyzing the tail-end behavior of a lithium cell having a solid cathode. The tail of a longer-term accelerated discharge data (ADD) test is estimated from the tail of two shorter-term ADD tests. This is accomplished by first comparing the discharge tails of shorter-term ADD tests and determining angles or rotation that correspond to Rdc growth, and then trending rotation angles versus time to reach a give DoD. For example, the 18-month and 36-month ADD test tails are used to estimate the ADD test tail of a similarly constructed cell subjected to a longer-term ADD test, for example a 48-month ADD test.
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Citations
15 Claims
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1. A method for estimating the discharge curve of an electrochemical cell, comprising the steps of:
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a) subjecting a first cell to a first shorter-term accelerated discharge test having a shortest total time on test, thereby generating a first discharge curve;
b) subjecting a second cell to a second shorter-term accelerated discharge test having a longer total time on test than the first cell, thereby generating a second discharge curve;
c) subjecting a third cell to a longer-term accelerated discharge test having a longer total time on test than either the first or second cells, thereby generating a third discharge curve, wherein the first, second and third cells are of a similar chemistry and construction;
d) offsetting the second and third discharge curves so that they intercept with the first discharge curve at a pre-determined similar percent depth-of-discharge;
e) calculating a first and second series of slopes for the first and second cells, respectively, from the intercept to an end percent depth-of-discharge at incremental depths-of-discharge;
f) calculating a rotational angle between the first and second series of slopes at each incremental depth-of-discharge; and
g) utilizing the rotational angles from step f) to estimate the third discharge curve from the intercept point to the end percent depth-of-discharge. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for estimating the discharge curve of an electrochemical cell, comprising the steps of:
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a) subjecting a first cell to a first shorter-term accelerated discharge test having a shortest total time on test, thereby generating a first discharge curve;
b) subjecting a second cell to a second shorter-term accelerated discharge test having a longer total time on test than the first cell, thereby generating a second discharge curve;
c) subjecting a third cell to a longer-term accelerated discharge test having a longer total time on test than either the first or second cells, thereby generating a third discharge curve, wherein the first, second and third cells are of a similar chemistry and construction;
d) offsetting the second and third discharge curves so that they intercept with the first discharge curve at a pre-determined similar percent depth-of-discharge;
e) shifting the intercept percent depth-of-discharge for the first, second and third cells to 0% depth-of-discharge;
f) calculating a first and second series of slopes for the first and second cells, respectively, from the shifted intercept to an end percent depth-of-discharge at incremental depths-of-discharge;
g) calculating a rotational angle between the first and second series of slopes at each incremental depth-of-discharge; and
h) utilizing the rotational angles from step g) to estimate the third discharge curve from the shifted intercept point to the end percent depth-of-discharge.
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15. A method for estimating when an electrochemical cell powering an implantable medical device will need to be replaced, comprising the steps of:
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a) subjecting a first cell to a first shorter-term accelerated discharge test having a shortest total time on test, thereby generating a first discharge curve;
b) subjecting a second cell to a second shorter-term accelerated discharge test having a longer total time on test than the first cell, thereby generating a second discharge curve;
c) subjecting a third cell to a longer-term accelerated discharge test having a longer total time on test than either the first or second cells, thereby generating a third discharge curve, wherein the first, second and third cells are of a similar chemistry and construction;
d) intercepting the first discharge curve with the second discharge curve at a pre-determined similar percent depth-of-discharge;
e) calculating a first and second series of slopes for the first and second cells, respectively, from the intercept to an end percent depth-of-discharge at incremental depths-of-discharge;
f) calculating a rotational angle between the first and second series of slopes at each incremental depth-of-discharge; and
g) utilizing the rotational angles from step f) to estimate a remaining portion of the third discharge curve past its intercept with the first and second discharge curves to the end percent depth-of-discharge thereby determining when the medical device will need to be replaced based on actual usage in a patient being similar to one of the first, second and third discharge curves.
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Specification